In general, this type of bottle is made from a synthetic resin such as polyethylene terephthalate and produced, for example, by blow molding. In recent years, the energy necessary for re-melting on recycling have been reduced to cope with environmental problems or materials have been used in a smaller quantity to save material costs. As a result, the bottle in itself has been made lighter in weight.
However, a bottle made lighter in weight decreases the rigidity. Therefore, for example, the bottom thereof is softened by heat resulting from a high-temperature liquid filled into the bottle. When the weight of the liquid acts on the thus softened bottom, a base portion installed on the outer circumference brim at the bottom of the bottle is deformed so as to swell toward the outside of the bottle, which may inhibit stability when the bottle is set upright, that is, uprightness. Alternatively, when a bottle, into which a high-temperature liquid is filled, is heated in order to impart sterilization, the internal pressure of the bottle is increased, thereby the base portion at the bottom of the bottle is deformed so as to swell outwardly, which may inhibit the uprightness of the bottle, as described above.
In order to solve the above problem, for example, the technology disclosed in Patent Document 1 given below may be adopted. Specifically, a plurality of hollow ribs protruding outside the bottle to extend in a radial direction are formed so as to be spaced at a predetermined interval in a circumferential direction at an annular recess located between the base portion of a bottle and a central recess installed at the center of the bottom of the bottle. Thereby, the compressive strength of the bottom of the bottle is increased.    PATENT DOCUMENT 1: Japanese Unexamined Patent Application, First Publication No. 2002-308245